1. Field of the Invention
The present invention relates to an image recording method and image recording apparatus for recording a desired image on a recording target, and in particular to a technology for recording a high-density image at high resolution.
2. Description of the Related Art
A color image recording method is known whereby a transfer sheet having color material layers of Black (K), Cyan (C), Magenta (M) and Yellow (Y) are sequentially overlaid on an image reception sheet having an image reception layer and the color material layers of each transfer sheet are transferred as an image to the image reception layer of the image reception sheet, then finally a latent image transferred to the image reception sheet is transferred to desired printing paper. Such a color image recording method uses as a recording target printing paper including woodfree paper and coat paper.
In case recording is made using typical printing inks via the aforementioned related art recording method, the density of K for example is sufficient as long as a light reflection density of about 1.8 (transmission density of about 0.9) is attained.
In case the aforementioned related art recording method is used to make recording on another recording target, unlike the case of recording on printing paper, there may arise a problem of an insufficient printing density. This occurs, in particular, in such applications as formation of a black matrix of a liquid crystal display and manufacturing of color filters.
A black matrix is a stripe-shaped light shield for shielding against leakage of light between display pixels to enhance the contrast. A color filter serves as a desired optical function layer for example on a transparent substrate to control the transmission wavelength band and typically deposited by an approach such as the photolithography.
In such a recording target, in particular for K, a light transmission density of about 3.0 is required. Thus, the aforementioned related art recording method has failed to assure a sufficient density.
Increasing a film thickness of a color material layer of a transfer sheet may increase the density. However, this also increases the minimum peel size from the sheet of color material layers thus dropping the resolution of a resulting image. By way of example, as shown in Table 4, it is demonstrated that a resolution is approximately proportional to the cube of a film thickness and a transmission density is proportional to a film thickness according to the related art recording method.
Thus, while a resolution of 5.0 xcexcm is attained with a film thickness of a color material layer of 0.50 xcexcm, the equivalent resolution has dropped to 40 xcexcm in case the film thickness is doubled, that is, for a film thickness of a color material layer of 1.00 xcexcm. This figure, 40 xcexcm, is virtually unacceptable.
The invention has been proposed in view of the aforementioned objects and aims at providing an image recording method and image recording apparatus for performing high-density recording without degrading the resolution.
In order to attain the aforementioned objects, an image recording method according to the first aspect of the invention is an image recording method for recording a desired image on a recording medium by exposing the image on the recording medium while moving the recording medium in the main scan direction wherein a toner layer of a transfer sheet is overlaid on an image reception layer of an image reception sheet as well as moving a plurality of laser beam spots arranged on the recording medium in the sub-scan direction orthogonal to the main scan direction, characterized in that a recording process on the transfer sheet is repeated a plurality of times to record a same image repeatedly with transfer sheets replaced after the transfer sheet has been exposed.
According to this image recording method, it is possible to obtain a target recording density by recording a same image a plurality of times with transfer sheets replaced thus repeating the image recording with a toner layer of a transfer sheet having a constant recording resolution while maintaining the film thickness of the toner layer.
An image recording method according to the second aspect of the invention is an image recording method for recording a desired image on the recording medium by using the transfer sheets of a plurality of different colors, comprising a transfer sheet supply process for supplying the transfer sheets of at least one of the colors to a recording section to overlay the sheets on the image reception sheet, an exposure process for exposing an image on the recording medium in the recording section based on desired image information, and a transfer sheet ejecting process for ejecting an exposed transfer sheet from the recording section, characterized in that the image recording method executes the transfer sheet supply process, the exposure process, and the transfer sheet ejecting process a plurality of times in a same color.
According to this image recording method, a transfer sheet supply process, an exposure process, and a transfer sheet ejecting process are repeated for separate transfer sheets of a same color a plurality of times on an image reception sheet supplied in advance in the recording section. Thus, it is made easy to use existing supply, recording, and ejection mechanisms to execute recording of a same image using separate transfer sheets of a same color a plurality of desired times. An exposed transfer sheet once used for recording is ejected and a new transfer sheet of the same color is supplied in the next recording cycle. This allows a toner layer containing a perfect image without loss to be deposited.
An image recording method according to the third aspect of the invention is characterized in that the image recording method repeats recording of an image of the same color with the minimum repetition recordings wherein the recording density accumulated by repeated recording exceeds a target recording density in case the standard recording density obtained by a single exposure is less than the target recording density.
According to this image recording method, recording density is cumulatively summed by repeating recording at a standard recording density. When a cumulative recording density has finally exceeded a target recording density, recording is terminated. Thus, it is possible to obtain a cumulative recording density greater than a target recording density with the minimum repetition recordings while repeating recording at a standard recording density.
An image recording method according to the fourth aspect of the invention is characterized in that the image recording method obtains an integer wherein the split recording density obtained by dividing a target recording density by the integer is maximum and lower than a standard recording density in case the standard recording density obtained by a single exposure is lower than the target recording density.
According to this image recording method, an integer is obtained so that the split recording density obtained by dividing a target recording density by the integer will be maximum and lower than a standard recording density. That is, repeating recording at the split recording density as many times as the integer obtained provides a recording density approximately identical with a target recording density. Thus, the cumulative recording density obtained at completion of a plurality of recordings is approximately identical with the target recording density. This avoids unnecessary recordings thus assuring economical image recording.
An image recording method according to the fifth aspect of the invention is characterized in that recording at a split recording density obtained by dividing a target recording density by the maximum number of repeated recordings allowed is repeated the maximum number of recordings, in case a standard recording density obtained by a single exposure is lower than the target recording density.
According to this image recording method, recording at a split recording density obtained by dividing a target recording density by the maximum number of repeated recordings allowed is repeated the maximum number of recordings. This reduces the number of repetitions required until the target recording density is attained thereby enhancing the productivity.
Image recording apparatus according to the sixth aspect of the invention is image recording apparatus for recording a desired image on a recording medium by exposing the image on the recording medium while moving the recording medium in the main scan direction wherein a toner layer of a transfer sheet is overlaid on an image reception layer of an image reception sheet as well as moving a plurality of laser beam spots arranged on the recording medium in the sub-scan direction orthogonal to the main scan direction, characterized in that the image recording apparatus comprises a controller for controlling exposure of the image on the transfer sheet based on an image recording method according to any one of the first through fifth aspects of the invention.
According to this image recording apparatus, it is possible to obtain a target recording density by control of recording a same image a plurality of times with transfer sheets replaced thus repeating the image recording with a toner layer of a transfer sheet having a constant recording resolution while maintaining the film thickness of the toner layer.